FOLDING A FILTER 127 



the creases on the side opposite to that occupied by creases 

 1, 2, 3, 4, etc., first made. As each of these folds is made 

 the paper is gradually brought into a wedge-shaped bundle 

 (Fig. 17, a), which when opened assumes the form of a 

 properly folded filter (seen in 6, Fig. 17). Before placing 

 it upon the funnel it is well to go over each crease and see 

 that it is as closely folded as possible, care being taken not 

 to tear it. The advantage of the folded filter is that by its 

 use a much greater filtering, surface is obtained, as it is in 

 contact with the funnel only at the points formed by the 

 ridges, leaving the greater part of the flat surface free for 



filtration. 



FIG. 17 



The employment of the hot-water funnel, so often recom- 

 mended, has been dispensed with in this work to a very 

 large extent, for the reason that if solution of the gelatin 

 is complete, filtration is so rapid as not to necessitate the 

 use of an apparatus for maintaining a high temperature. 

 The temperature at which the hot-water funnel retains the 

 gelatin is so high that evaporation and concentration rapidly 

 occur, and in consequence filtration is, as a rule, retarded. 

 The filtration is frequently done in the steam sterilizer; 

 but this, too, is unnecessary if the gelatin is quite dissolved. 

 At the ordinary temperature of the room, and by the means 

 commonly employed for the filtration of other substances, 



